(1) Field of the Invention
The present invention relates to a display device and particularly, to a display region capable of forming an electrostatic protection circuit in a narrow region.
(2) Description of the Related Art
In liquid crystal display devices being one kind of display devices, there are arranged a TFT substrate on which pixels having pixel electrodes and thin film transistors (TFTs) are formed in a matrix fashion, and an opposite substrate facing the TFT substrate, and a liquid crystal layer is provided with itself between the TFT substrate and the opposite substrate. Then, an image is formed by controlling the transmission factors of light through liquid crystal molecules on a pixel-by-pixel basis.
The liquid crystal display device is formed with a TFT for each of the pixels, and a scanning line drive circuit and the like having many TFTs is formed outside the display region. When static electricity invades from outside, a TFT is destroyed by the static electricity to cause the liquid crystal display device fall in failure. In order to prevent this, there is arranged an electrostatic protection circuit. The electrostatic protection circuit is called ESD (Electro Static Discharger) in some cases. International Application Publication WO-A1-2010147032 describes a configuration that uses resistances and diodes for the ESD circuit in a display device. Further, Japanese Patent Application Publication No. 2009-37124 A1 discloses a display device with an electrostatic protection circuit.
In liquid crystal display devices of medium to small sizes, it has been strongly requested to make the size of a display region large with the external size remained small. If such is done, a frame region outside the display region becomes small. On one hand, an electrostatic protection circuit is essential for the protection of TFTs used in the liquid crystal display device. In order to maintain the sensitivity of the electrostatic protection circuit high, a certain degree of size is required for the TFTs used in the electrostatic protection circuit.
On the other hand, the electrostatic protection circuit is formed in a frame region, and thus, for a small frame region, it is necessary to make small the area used for the electrostatic protection circuit. However, there arises a dilemma that making the area occupied by the electrostatic protection circuit small generally results in lowering the sensitivity of the electrostatic protection circuit.